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31bf3874d6
Use of reflect.Value.SetXXX panics if the provided argument was obtained from an unexported struct field. Instead, pass an unsafe.Pointer around and convert to a reflect.Value when necessary (i.e., for maps and interfaces). Converting from unsafe.Pointer to reflect.Value guarantees that none of the read-only bits will be populated. When running in race mode, we attach type information to the pointer so that we can type check every pointer operation. This also type-checks that direct memory hashing is within the valid range of a struct value. We add test cases that previously caused deephash to panic, but now pass. Performance: name old time/op new time/op delta Hash 14.1µs ± 1% 14.1µs ± 1% ~ (p=0.590 n=10+9) HashPacketFilter 2.53µs ± 2% 2.44µs ± 1% -3.79% (p=0.000 n=9+10) TailcfgNode 1.45µs ± 1% 1.43µs ± 0% -1.36% (p=0.000 n=9+9) HashArray 318ns ± 2% 318ns ± 2% ~ (p=0.541 n=10+10) HashMapAcyclic 32.9µs ± 1% 31.6µs ± 1% -4.16% (p=0.000 n=10+9) There is a slight performance gain due to the use of unsafe.Pointer over reflect.Value methods. Also, passing an unsafe.Pointer (1 word) on the stack is cheaper than passing a reflect.Value (3 words). Performance gains are diminishing since SHA-256 hashing now dominates the runtime. Signed-off-by: Joe Tsai <joetsai@digital-static.net>
15 lines
398 B
Go
15 lines
398 B
Go
// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build !race
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package deephash
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import "reflect"
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type pointer = unsafePointer
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// pointerOf returns a pointer from v, which must be a reflect.Pointer.
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func pointerOf(v reflect.Value) pointer { return unsafePointerOf(v) }
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